This invention relates to a pen changing apparatus for a plotter, and more particularly to a pen changing apparatus suitable for a plotter composed of a plurality of pens mounted on a carriage.
Conventionally, there are two types of pen changing apparatus for a plotter composed of a plurality of pens mounted on a carriage; one is a pen changing apparatus of the type which consists of pen driving portions of an appropriate number corresponding to the number of pens wherein the appropriate pen driving portions are selected for the purpose of moving the relevant pens up and down and changing them, as is shown in FIGS. 1 and 2; and the other is a pen changing apparatus of the type which consists of a rotatable pen holder with a plurality of pens attached thereto wherein pens are changed by rotating the holder, as is shown in FIG. 3.
Referring to FIG. 1, four pens 1a to 1d are attached to the respective arms 2a to 2d and are moved up and down with an arm supporting point 3 as their axis of rotation. Solenoids 4a to 4d for driving the relevant pens 1a to 1d are attached to the arms 2a to 2d, respectively, on the opposite side of the pens 1a to 1d so as to attract or release the arms 2a to 2d in accordance with an electrical signal "ON" or "OFF". In the example shown in FIG. 1, when the solenoids 4a to 4d are in the "ON" state, the pens 1a to 1d are raised away from the paper, and when they are in the "OFF" state, the pens 1a to 1d are lowered such as to come into contact with the paper by return springs 5a to 5d. That is, by selecting a solenoid to which a signal is to be sent, it is determined which pen is to be moved up and down. However, when pens are changed, a shifting operation by a degree corresponding to he interval between pens is necessary in order to equalize the original point of each pen. Further a carriage 6 must slide on the shafts 7 and 8 with the plurality of pens 1a to 1d and the solenoids 4a to 4d mounted thereon. The referential numeral 9 denotes a solenoid wiring and 10 a string for moving the carriage 6.
An apparatus of this type has the following disadvantages. Since each pen requires one solenoid as its driving portion, the number, and hence the weight of parts such as solenoids and arms which are mounted on the carriage 6 is increased and wiring becomes complicated. Furthermore, not only is the driving load of the carriage increased but also the manufacturing cost is raised significantly.
FIG. 2 is a sectional view of another example of a pen driving device, which shows one pen a plurality of pens. The referential numeral 20 represents a pen, 21 a pen lifting spring, 22 a carriage, 23 a solenoid, and 24 solenoid wiring. There is nothing corresponding to the arm in FIG. 1, and the pen 20 is directly driven by the solenoid 23. In this case also, the following problems remain unsolved. Since the pen 20 is driven by the solenoid 23, the required number of solenoids 23 equals that of pens 20. Since it is necessary to coat the pen 20 with a magnetic material, the cost of the pen 20 is raised. It is necessary to heighten the accuracy of the sliding surface of the pen 20. In addition, in order to have the solenoid 23 built-in, the structure of the carriage 22 becomes complicated and thus expensive.
Referring to FIG. 3, the referential numerals 31a to 31d represent pens, 32 a rotary holder, 33a, 33b, . . . projections which are provided at regular intervals on the outer peripheral portion of the rotary holder 32, 35 a carriage, 36, 37 shafts, 38 a frame, 39 a pin, 40a, 40b supporting points, 41 a pen lever, 42 a solenoid, 43 a return spring, and 44 a string. The pens 31a to 31d are attached to the outer periphery of the rotary holder 32 at equal intervals. The rotary holder 32 rotates around the rotary shaft 34 and the pens 31a to 31d are retained at equal intervals by a spring, a ratchet (not shown), and so forth. The rotary holder 32 slides in the axial direction of the shafts 36, 37 together with the carriage 35. A desired pen (in the FIG. 31c) is moved up and down when the pen lever 41 is raised and lowered by means of the solenoid 42 and the return spring 43. When an instruction for changing pens is received, the carriage 35 travels in the direction indicated by the arrow a, and one of the projections 33a, 33b, . . . which are provided at regular intervals on the outer periphery of the rotary holder 32 hits the pin 39 which protrudes from the frame 38, whereby the rotary holder 32 rotates in the direction indicated by the arrow b. After the holder 32 is rotated through a certain angle, the carriage 35 is moved in the opposite direction indicated by the arrow a. This operation is repeated until the desired pen comes to the position of the pen 31c, and the pens are then changed. According to this system, only one driving portion consisting of the solenoid 42 suffices, but a mechanism is required for smoothly rotating the rotary holder 32 and retaining each of the pens 31a to 31d at equal intervals by means of a ratchet and so forth. Therefore, disadvantageously, the structure becomes complicated, and changing pens takes much time because several reciprocating motions of the carriage 35 are necessary for each pen changing operation.